metal, chemical element element, in chemistry, a substance that cannot be decomposed into simpler substances by chemical means. A substance such as a compound can be decomposed into its constituent elements by means of a chemical reaction, but no further simplification can be achieved.
..... Click the link for more information. displaying certain properties by which it is normally distinguished from a nonmetal, notably its metallic luster, the capacity to lose electrons and form a positive ion ion, atom or group of atoms having a net electric charge .

Positive and Negative Electric Charges

A neutral atom or group of atoms becomes an ion by gaining or losing one or more electrons or protons.
..... Click the link for more information. , and the ability to conduct heat and electricity. The metals comprise about two thirds of the known elements (see periodic table periodic table, chart of the elements arranged according to the periodic law discovered by Dmitri I. Mendeleev and revised by Henry G. J. Moseley . In the periodic table the elements are arranged in columns and rows according to increasing atomic number (see the
..... Click the link for more information. ). Some metals, including copper, tin, iron, lead, gold, silver, and mercury, were known to the ancients; copper is probably the oldest known metal.

Physical Properties

Metals differ so widely in hardness, ductility (the potentiality of being drawn into wire), malleability, tensile strength, density, and melting point that a definite line of distinction between them and the nonmetals nonmetal, chemical element possessing certain properties by which it is distinguished from a metal . In general, this distinction is drawn on the basis that a nonmetal tends to accept electrons and form negative ions and that its oxide is acidic.
..... Click the link for more information. cannot be drawn. The hardest elemental metal is chromium; the softest, cesium. Copper, gold, platinum, and silver are especially ductile. Most metals are malleable; gold, silver, copper, tin, and aluminum are extremely so. Some metals exhibiting great tensile strength are copper, iron, and platinum. Three metals (lithium, potassium, and sodium) have densities of less than one gram per cubic centimeter at ordinary temperatures and are therefore lighter than water. Some heavy metals, beginning with the most dense, are osmium, iridium, platinum, gold, tungsten, uranium, tantalum, mercury, hafnium, lead, and silver.

For many industrial uses, the melting points of the metals are important. Tungsten fuses, or melts, only at extremely high temperatures (3,370°C;.), while cesium has a melting point of 28.5°C;. The best metallic conductor of electricity is silver. Copper, gold, and aluminum follow in the order named. All metals are relatively good conductors of heat; silver, copper, and aluminum are especially conductive. The radioactive metal uranium is used in reactor piles to generate steam and electric power. Plutonium, another radioactive element, is used in nuclear weapons and nuclear reactors as well as in pacemakers. Some of the radioactive metals not found in nature, e.g., fermium and seaborgium, are produced by nuclear bombardment.

Some elements, e.g., arsenic and antimony, exhibit both metallic and nonmetallic properties and are called metalloids. Furthermore, although all metals form crystals, this is also characteristic of certain nonmetals, e.g., carbon and sulfur.

Chemical Properties

Chemically, the metals differ from the nonmetals in that they form positive ions and basic oxides and hydroxides. Upon exposure to moist air, a great many undergo corrosion, i.e., enter into a chemical reaction; e.g., iron rusts when exposed to moist air, the oxygen of the atmosphere uniting with the metal to form the oxide of the metal. Aluminum and zinc do not appear to be affected, but in fact a thin coating of the oxide is formed almost at once, stopping further action and appearing unnoticeable because of its close resemblance to the metal. Tin, lead, and copper react slowly under ordinary conditions. Silver is affected by compounds such as sulfur dioxide and becomes tarnished when exposed to air containing them. The metals are combined with nonmetals in their salts, as in carbides, carbonates, chlorides, nitrates, phosphates, silicates, sulfides, and sulfates.

The Electromotive Series

On the basis of their ability to be oxidized, i.e., lose electrons, metals can be arranged in a list called the electromotive series electromotive series, list of metals whose order indicates the relative tendency to be oxidized, or to give up electrons (see oxidation and reduction ); the list also includes the gas hydrogen. The electromotive series begins with the metal most easily oxidized, i.e.
..... Click the link for more information. , or replacement series. Metals toward the beginning of the series, like cesium and lithium, are more readily oxidized than those toward the end, like silver and gold. In general, a metal will replace any other metal, or hydrogen, in a compound that it precedes in the series, and under ordinary circumstances it will be replaced by any metal, or hydrogen, that it follows.

Metals in the Periodic Table

Metals fall into groups in the periodic table determined by similar arrangements of their orbital electrons electron, elementary particle carrying a unit charge of negative electricity. Ordinary electric current is the flow of electrons through a wire conductor (see electricity ). The electron is one of the basic constituents of matter.
..... Click the link for more information. and a consequent similarity in chemical properties. Groups of similar metals include the alkali metals alkali metals, metals found in Group 1 of the periodic table . Compared to other metals they are soft and have low melting points and densities. Alkali metals are powerful reducing agents and form univalent compounds.
..... Click the link for more information. (Group 1 in the periodic table), the alkaline-earth metals alkaline-earth metals, metals constituting Group 2 of the periodic table . Generally, they are softer than most other metals, react readily with water (especially when heated), and are powerful reducing agents, but they are exceeded in each of these properties by the
..... Click the link for more information. (Group 2 in the periodic table), and the rare-earth metals rare-earth metals, in chemistry, group of metals including those of the lanthanide series and actinide series , usually yttrium , sometimes scandium and thorium , and rarely zirconium .
..... Click the link for more information. (the lanthanide lanthanide series, a series of metallic elements, included in the rare-earth metals , in Group 3 of the periodic table . Members of the series are often called lanthanides, although lanthanum (atomic number 57) is not always considered a member of the series.
..... Click the link for more information. and actinide series actinide series, a series of radioactive metallic elements in Group 3 of the periodic table . Members of the series are often called actinides, although actinium (at. no. 89) is not always considered a member of the series.
..... Click the link for more information. of Group 3). Most metals other than the alkali metals and the alkaline earth metals are called transition metals (see transition elements transition elements or transition metals, in chemistry, group of elements characterized by the filling of an inner d electron orbital as atomic number increases.
..... Click the link for more information. ). The oxidation states, or valence valence, combining capacity of an atom expressed as the number of single bonds the atom can form or the number of electrons an element gives up or accepts when reacting to form a compound.
..... Click the link for more information. , of the metal ions vary from +1 for the alkali metals to as much as +7 for some transition metals.

Sources and Uses

Although a few metals occur uncombined in nature, the great majority are found combined in their ores ore, metal-bearing mineral mass that can be profitably mined. Nearly all rock deposits contain some metallic minerals, but in many cases the concentration of metal is too low to justify mining the ore.
..... Click the link for more information. . The separation of metals from their ores is called extractive metallurgy metallurgy (mĕt`əlûr'jē), science and technology of metals and their alloys .
..... Click the link for more information. . Metals are mixed with each other in definite amounts to form alloys alloy (ăl`oi, əloi`) [O. Fr.
..... Click the link for more information. ; a mixture of mercury and another metal is called an amalgam amalgam (əmăl`gəm), alloy containing mercury .
..... Click the link for more information. . Bronze bronze, in metallurgy, alloy of copper, tin, zinc, phosphorus, and sometimes small amounts of other elements. Bronzes are harder than brasses . Most are produced by melting the copper and adding the desired amounts of tin, zinc, and other substances.
..... Click the link for more information. is an alloy of copper and tin, and brass brass, alloy having copper (55%–90%) and zinc (10%–45%) as its essential components. The properties of brass vary with the proportion of copper and zinc and with the addition of small amounts of other elements, such as aluminum, lead, tin, or nickel.
..... Click the link for more information. contains copper and zinc. Steel steel, alloy of iron, carbon, and small proportions of other elements. Iron contains impurities in the form of silicon, phosphorus, sulfur, and manganese; steelmaking involves the removal of these impurities, known as slag, and the addition of desirable alloying
..... Click the link for more information. is an alloy of iron and other metals with carbon added for hardness.

Since metals form positive ions readily, i.e., they donate their orbital electrons, they are used in chemistry as reducing agents (see oxidation and reduction oxidation and reduction, complementary chemical reactions characterized by the loss or gain, respectively, of one or more electrons by an atom or molecule. Originally the term oxidation
..... Click the link for more information. ). Finely divided metals or their oxides are often used as surface catalysts catalyst, substance that can cause a change in the rate of a chemical reaction without itself being consumed in the reaction; the changing of the reaction rate by use of a catalyst is called catalysis.
..... Click the link for more information. . Iron and iron oxides catalyze the conversion of hydrogen and nitrogen to ammonia in the Haber process Haber process (hä`bər), commercial process for the synthesis of ammonia , NH₃.
..... Click the link for more information. . Finely divided catalytic platinum or nickel is used in the hydrogenation hydrogenation (hīdrôj`ənā'shən, hī'drəjənā`shən)
..... Click the link for more information. of unsaturated oils. Metal ions orient electron-rich groups called ligands ligand (lĭg`ənd), charged or uncharged molecule with one or more unshared pairs of electrons that can attach to a central metallic
..... Click the link for more information. around themselves, forming complex ions complex ion, charged molecular aggregate (see ion ), consisting of a metallic atom or ion to which is attached one or more electron-donating molecules. In some complex ions, such as sulfate, SO₄⁻²
..... Click the link for more information. . Metal ions are important in many biological functions, including enzyme enzyme, biological catalyst . The term enzyme comes from zymosis, the Greek word for fermentation , a process accomplished by yeast cells and long known to the brewing industry, which occupied the attention of many 19th-century chemists.
..... Click the link for more information. and coenzyme biotin, is a member of the B complex; it was first isolated in 1935 from dried egg yolk, and its structure was established in 1942. Biotin is usually found attached to a lysine residue in certain enzymes, where it participates in reactions involving the transfer of carboxyl
..... Click the link for more information. action, nucleic acid nucleic acid, any of a group of organic substances found in the chromosomes of living cells and viruses that play a central role in the storage and replication of hereditary information and in the expression of this information through protein synthesis.
..... Click the link for more information. synthesis, and transport across membranes.

For the uses of specific metals, see separate articles.

metal

Any of a class of substances with, to some degree, the following properties: good heat and electricity conduction, malleability, ductility, high light reflectivity, and capacity to form positive ions in solution and hydroxides rather than acids when their oxides meet water. About three-quarters of the elements are metals; these are usually fairly hard and strong crystalline (see crystal) solids with high chemical reactivity that readily form alloys with each other. Metallic properties increase from lighter to heavier elements in each vertical group of the periodic table and from right to left in each row. The most abundant metals are aluminum, iron, calcium, sodium, potassium, and magnesium. The vast majority are found as ores rather than free. The cohesiveness of metals in a crystalline structure is attributed to metallic bonding: The atoms are packed close together, with their very mobile outermost electrons all shared throughout the structure. Metals fall into the following classifications (not mutually exclusive and most not rigidly defined): alkali metals, alkaline earth metals, transition elements, noble (precious) metals, platinum metals, lanthanide (rare earth) metals, actinide metals, light metals, and heavy metals. Many have essential roles in nutrition or other biochemical functions, often in trace amounts, and many are toxic as both elements and compounds (see mercury poisoning, lead poisoning).

1.		METAL - Mega-Extensive Telecommunications Applications Language. BBS language for PRODOS 8 on Apple II.
2.		METAL - The syntax-definition formalism of the Mentor system. Metal specifications are compiled to specifications for a scanner/parser generator such as Lex/Yacc. "Metal: A Formalism to Specify Formalisms", G. Kahn et al, Sci Comp Prog 3:151-188 (1983).